# Summary

• A set is a collection of well defined objects.
• A set which does not contain any element is called an empty set.
• A set with definite number of elements is called finite set and if not it is called infinite set.
• Two sets are said to be equal if they have exactly the same elements.
• Set A is said to be subset of set B, if every element of the set A is also an element of the set B. Intervals are subsets of R.
• A power set of a set A is the collection of all the subsets of the set A. It is denoted as P(A).
• The set of all the elements which are either in A or in B is the union of two sets A and B.
• The set of all elements which are common in both the sets A and B is the intersection of the two sets.
• The set A - B is the set of all elements in A but not in B.
• The complement of a subset A of universal set U, denoted as A' is the set of all elements of U which are not the elements of A.
• (A âˆª B)' = A' âˆ© B' and (A âˆ© B)' = A' âˆª B' for any two sets A and B.
• If A and B are finite sets such that A âˆ© B = Ï†, n(A âˆª B) = n(A) + n (B). If A and B are not disjoint sets, n(A âˆª B) = n(A) + n (B) - n(A âˆ© B).